1. Field of the Invention
The present invention generally relates to a method and apparatus for controlling an automatic transmission in the absence of a driving mode signal from a driving mode sensor.
2. Description of the Related Art
Vehicles equipped with an automatic transmission typically have several driving modes. Those driving modes generally include park (P), reverse (R), neutral (N), drive (D), and lower speed ranges. The vehicle is equipped with a driving mode select lever by which a driver can select one of the driving modes P, R, N, D, etc. A driving mode sensor generates a signal indicating which of the driving modes the vehicle operator has selected. For example, a potentiometer can serve as the driving mode sensor, wherein the resistance changes as the driving mode select lever changes position.
As the driving mode select lever is moved from one driving mode to the other, the driving mode sensor outputs a signal indicating each driving mode. For instance, as the driving mode select lever is moved from park to drive, the driving mode sensor indicates the driving modes of park, reverse, neutral, and then drive. The driving mode sensor, however, can become damaged or malfunction. As a result, the driving mode sensor may fail to output a signal indicating a particular driving mode, may simultaneously output signals indicating two different driving modes, or may fail to output any type of driving signal at all.
The transmission control unit (TCU) of conventional automatic transmissions include methodologies for determining the driving mode when such driving mode sensor errors occur. When the conventional TCU fails to receive driving mode signals indicating driving modes between the driving modes indicated by two sequentially received driving mode signals, the conventional TCU determines the driving mode as the driving mode indicated by the last received driving mode signal. For instance, if the conventional TCU receives a driving mode signal indicating park and then a driving mode signal indicating drive without having received driving signals indicating reverse and neutral before the driving signal indicating drive, then the conventional TCU determines that the driving mode is drive.
If the conventional TCU receives a driving mode signal, and thereafter receives no driving mode signal or receives two different driving mode signals simultaneously, then the conventional TCU will select as the driving mode, the driving mode indicated by the previously received driving mode signal. For instance, if the conventional TCU receives a driving mode signal indicating park, and then receives no driving mode signal, or receives driving mode signals indicating neutral and drive simultaneously, then the conventional TCU selects park as the driving mode.
Furthermore, if after starting the vehicle, the conventional TCU receives no driving mode signal, then the conventional TCU selects neutral as the driving mode. Unfortunately, once the driver starts the vehicle, the driver typically moves the driving mode select lever to either reverse or drive. Because of gravity, the vehicle often tends to begin moving in the direction corresponding to the selected driving mode. Thereafter, the driver depresses the accelerator pedal. Because the conventional TCU selects neutral when no driving mode signal is received, the engine merely revs up. This can be very disconcerting to the driver.